Betting on Consensus with Fantmette Sarah Azouvi, Patrick McCorry, - - PowerPoint PPT Presentation

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Betting on Consensus with Fantmette Sarah Azouvi, Patrick McCorry, - - PowerPoint PPT Presentation

Aug 15, 2022 259 likes •1.18k views

Betting on Consensus with Fantmette Sarah Azouvi, Patrick McCorry, Sarah Meiklejohn University College London CESC 2018, SF , October 11 2018 1 Bitcoin vs Traditional Consensus Bitcoin vs Traditional Consensus Open, participants

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Betting on Consensus with Fantômette

Sarah Azouvi, Patrick McCorry, Sarah Meiklejohn University College London

  • 1

CESC 2018, SF , October 11 2018

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Bitcoin vs Traditional Consensus

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  • Open, participants unknown

Bitcoin vs Traditional Consensus

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  • Open, participants unknown
  • One message broadcast per round

Bitcoin vs Traditional Consensus

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  • Open, participants unknown
  • One message broadcast per round
  • Incentives at the core of its security

Bitcoin vs Traditional Consensus

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  • Open, participants unknown
  • One message broadcast per round
  • Incentives at the core of its security
  • High energy consumption

Bitcoin vs Traditional Consensus

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Blockchain without PoW?

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Blockchain without PoW?

  • Proof-of-stake: computation stake
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Blockchain without PoW?

  • Proof-of-stake: computation stake
  • Can we get the same guarantees?
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Blockchain without PoW?

  • Proof-of-stake: computation stake
  • Can we get the same guarantees?
  • Problems: nothing at stake, grinding, long range attacks
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Blockchain without PoW?

  • Proof-of-stake: computation stake
  • Can we get the same guarantees?
  • Problems: nothing at stake, grinding, long range attacks
  • Proposed solutions: PBFT style (e.g. Algorand),

cryptographic (e.g. Ouroboros, Snow-White)

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Blockchain without PoW?

  • Proof-of-stake: computation stake
  • Can we get the same guarantees?
  • Problems: nothing at stake, grinding, long range attacks
  • Proposed solutions: PBFT style (e.g. Algorand),

cryptographic (e.g. Ouroboros, Snow-White)

  • Incentives rarely considered
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Incentives matter

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Incentives matter

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Incentives matter

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Incentives matter

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Incentives matter

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Incentives matter

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Incentives matter

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Model

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Model

Rational Players

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Model

Rational Players Byzantine (Malicious) Players

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Model

Rational Players Byzantine (Malicious) Players Coalitions

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Model

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Model

BAR Model

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Model

BAR Model

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Model

BAR Model

Byzantine Altruistic Rational

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Model

BAR Model

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Model

BAR Model Robustness

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Model

BAR Model Robustness

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Model

BAR Model Robustness

Resilience

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Model

BAR Model Robustness

Resilience Immunity

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Model

Rational Players Byzantine (Malicious) Players Coalitions

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Model

Rational Players Byzantine (Malicious) Players Coalitions

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Model

Rational Players Byzantine (Malicious) Players Coalitions

  • Chain growth
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Model

Rational Players Byzantine (Malicious) Players Coalitions

  • Chain growth
  • Chain quality
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Model

Rational Players Byzantine (Malicious) Players Coalitions

  • Chain growth
  • Chain quality
  • Common prefix
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Fantômette

Overview

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Fantômette

Overview Leader Election

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Fantômette

Overview Leader Election Instead of PoW: leader election

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Fantômette

Overview Leader Election Instead of PoW: leader election Publicly Verifiable Proof of Eligibility

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Fantômette

Overview Leader Election One block elects at least one leader Instead of PoW: leader election Publicly Verifiable Proof of Eligibility

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Fantômette

Overview Leader Election One block elects at least one leader Betting Scheme Instead of PoW: leader election Publicly Verifiable Proof of Eligibility

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Fantômette

Overview Leader Election One block elects at least one leader Betting Scheme Use incentives to move away from BFT-style Instead of PoW: leader election Publicly Verifiable Proof of Eligibility

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Fantômette

Continuous Leader Election

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Fantômette

Continuous Leader Election

  • Fair (Chain quality)
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Fantômette

Continuous Leader Election

  • Fair (Chain quality)
  • Unpredictable
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Fantômette

Continuous Leader Election

  • Fair (Chain quality)
  • Unpredictable
  • Privately unpredictable
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Fantômette

Continuous Leader Election

  • Fair (Chain quality)
  • Unpredictable
  • Privately unpredictable
  • Liveness
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Fantômette

Continuous Leader Election

Random beacon

Pseudo-randomly generated number associated within each block

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Fantômette

Continuous Leader Election

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Fantômette

Continuous Leader Election

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Fantômette

Continuous Leader Election

Initial Random Beacon Verifiable Random Function < target?

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Fantômette

Continuous Leader Election

Initial Random Beacon Verifiable Random Function < target? Verifiable Delay Function -> liveness

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Fantômette

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Fantômette

  • blockDAG (PHANTOM Sompolinski & Zohar)
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Fantômette

  • blockDAG (PHANTOM Sompolinski & Zohar)
  • A block bets on its parent block
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Fantômette

  • blockDAG (PHANTOM Sompolinski & Zohar)
  • A block bets on its parent block
  • A block references other blocks
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Fantômette

  • blockDAG (PHANTOM Sompolinski & Zohar)
  • A block bets on its parent block
  • A block references other blocks

Genesis block A B C

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Fantômette

  • blockDAG (PHANTOM Sompolinski & Zohar)
  • A block bets on its parent block
  • A block references other blocks

Genesis block A B C Notion of chain

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G A B C D

Fantômette

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G A B C D

Fantômette

  • More connection = better score
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G A B C D

Fantômette

  • More connection = better score
  • Break tie with the random beacon
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G A B C D

Fantômette

  • More connection = better score
  • Break tie with the random beacon
  • Can only reference blocks with smaller score
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G A B C D

Fantômette

  • More connection = better score
  • Break tie with the random beacon
  • Can only reference blocks with smaller score
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G A B C D

Fantômette

  • More connection = better score
  • Break tie with the random beacon
  • Can only reference blocks with smaller score
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G A B C D

Main chain grows faster

Fantômette

  • More connection = better score
  • Break tie with the random beacon
  • Can only reference blocks with smaller score
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Fantômette

G A B C D

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Fantômette

G A B C D E

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Fantômette

G A B C D E

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Fantômette

G A B C D E F

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Fantômette

G A B C D E F

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Fantômette

G A B C D E F Reward connectivity

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Fantômette

G A B C D E F Reward connectivity Punishment if not well connected

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Security

Robustness

More likely to win when following the protocol Publish block as fast as possible to get more references Incentive to reference other blocks

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Security

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Security

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Security

Convergence Chain Growth Common prefix

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Security

Convergence Score of the main chain grows faster Chain Growth Common prefix

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Security

Convergence Chain quality Score of the main chain grows faster Chain Growth Common prefix

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Security

Convergence Chain quality Fair leader election Score of the main chain grows faster Chain Growth Common prefix

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Decentralized Checkpointing

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Decentralized Checkpointing

Genesis block X1 X2 Y1 Y2 Z1 Z2

2/3+ 2/3+

. . . . . . . . . . . .

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Decentralized Checkpointing

Genesis block X1 X2 Y1 Y2 Z1 Z2

2/3+ 2/3+

. . . . . . . . . . . .

Candidate Blocks

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Decentralized Checkpointing

Genesis block X1 X2 Y1 Y2 Z1 Z2

2/3+ 2/3+

. . . . . . . . . . . .

x1 and x2 are justified Candidate Blocks

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Decentralized Checkpointing

Genesis block X1 X2 Y1 Y2 Z1 Z2

2/3+ 2/3+

. . . . . . . . . . . .

x1 and x2 are justified x1 and x2 are finalized Candidate Blocks

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Simulations

payoff for altruistic players payoff for coalition of rational players payoff for altruistic players payoff for coalition of Byzantine players

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Simulations

Longest fork Chain Quality

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Conclusion

  • blockDAG : enforce accountability
  • Incentivize rational players to follow the protocol
  • Leverage incentive to have a blockchain type pos

consensus

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pre-print: https://arxiv.org/abs/1805.06786

Fantômette

sarah.azouvi.13@ucl.ac.uk @SarahAzouvi

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pre-print: https://arxiv.org/abs/1805.06786

Fantômette

Questions?

sarah.azouvi.13@ucl.ac.uk @SarahAzouvi